This invention relates to a welding current measuring apparatus intended to provide welding quality control for a resistance welding machine, and more particularly to such a measuring apparatus which allows the measurement of currents or the display of current waveforms in a given cycle interval by specifying the desired interval after completion of welding so as to trace the origin of poor welds, if any, over all energizing cycle intervals.
There is a conventional welding current measuring apparatus disclosed in Japanese Patent Publication No. 56-37037 entitled "Welding Current Monitoring Method and Apparatus."
Such a conventional welding current measuring method comprises the steps of; specifying an optional welding current sampling interval before the energization for welding and comparing a cumulative mean current in the desired sampling interval with a predetermined reference current value in order to judge the welding current intensity.
However, the conventional apparatus has the following shortcomings.
Since desired welding current sampling interval must be specified prior to energization for welding, i.e., before the current is measured, currents caused to flow in cycle intervals other than the specified one are ignored and thus are unmeasurable. It is often necessary to make the currents or current waveforms in the ignored intervals after completion of welding clear so as to trace the origin of a poor weld, if there are any. In that case, the only measure conventionally taken comprises again specifying the sampling interval and the reference current for the welding current monitoring level and attempting welding under the conditions assumed to be the same as those for the previous time. However, no complete reproducibility is guaranteed and there have been increasing difficulties in tracing the origins of poor welds.